In a conventional vehicle engine, a torsional damper which reduces torsional vibrations induced by rotational fluctuations of a crankshaft is attached to one end of the crankshaft.
Generally, a torsional damper is used as a damper pulley in an engine of a vehicle and transmits a portion of power from the engine to an auxiliary machine, such as a water pump or an air-conditioner compressor, via a belt for power transmission. A space between the torsional damper and, for example, a through hole in a front cover, through which a crankshaft is inserted, is sealed with an oil seal.
FIG. 7 is a partial sectional view in cross-section along an axis for schematically showing a sealing structure which is used in an engine of a vehicle and uses a conventional damper pulley 100 of a single-mass type and an oil seal 110. As shown in FIG. 7, the conventional damper pulley 100 includes a hub 101 in an annular shape which is made of metal, a pulley 102 which functions as a damper mass, and a damper elastic body 103 which is disposed between the hub 101 and the pulley 102.
The hub 101 includes a boss portion 101a on an inner periphery side, a rim portion 101b on an outer periphery side, and a disk portion 101c which connects the boss portion 101a and the rim portion 101b. The boss portion 101a of the hub 101 is fitted on a stepped portion at one end of a crankshaft 120 and is fixed with a bolt 121. A plurality of window portions 101d which are each composed of a through hole extending through the disk portion 101c are formed in a circumferential direction in the disk portion 101c in order to reduce weight.
The boss portion 101a of the hub 101 attached to the crankshaft 120 is in a state of being inserted through a through hole 123 in a front cover 122 of the engine from outside the engine.
The oil seal 110 is press fitted in the through hole 123 between the boss portion 101a and the front cover 122. A seal lip 111 of the oil seal 110 abuts slidably and liquid-tightly on an outer peripheral surface of the boss portion 101a and hermetically seals a void between the damper pulley 100 and the front cover 122.
FIG. 8 is a partial sectional view in cross-section along an axis for schematically showing a sealing structure with a conventional damper pulley 200 of a double-mass type and an oil seal 210. As shown in FIG. 8, the damper pulley 200 of the double-mass type is generally used for the purpose of reducing torsional vibrations induced by rotational fluctuations of a crankshaft 220 to a greater degree than the single-mass type.
In the damper pulley 200, sleeves 202 and 203 in annular shapes which are made of sheet metal are attached to fit on an inner periphery side and an outer periphery side, respectively, of a rim portion 201b of a hub 201 in an annular shape which is made of metal. Metal mass bodies 206 and 207 are attached to the sleeves 202 and 203 via rubber-like elastic bodies 204 and 205 in annular shapes, respectively.
In this case, the mass body 206 functions as an inner mass, and the mass body 207 functions as an outer mass. That is, the damper pulley 200 has a double-mass structure with the mass body 206 as the inner mass and the mass body 207 as the outer mass. The rubber-like elastic bodies 204 and 205 are vulcanized and bonded to the sleeves 202 and 203 and the mass bodies 206 and 207 concurrently with molding of the rubber-like elastic bodies 204 and 205.
The oil seal 210 is press fitted in a through hole 233 between a boss portion 201a of the hub 201 and a front cover 230. A seal lip 211 of the oil seal 210 abuts slidably and liquid-tightly on an outer peripheral surface of the boss portion 201a and hermetically seals a void between the damper pulley 200 and the front cover 230 (see, for example, Japanese Utility Model Application Publication No. 07-10582).
FIG. 9 is a partial sectional view in cross-section along an axis for schematically showing a sealing structure which is used in an engine of a vehicle and uses a conventional damper pulley 1100 of a single-mass type and an oil seal 1110. As shown in FIG. 9, the conventional damper pulley 1100 includes a hub 1101 in an annular shape which is made of metal, a pulley 1102 which functions as a damper mass, and a damper elastic body 1103 which is disposed between the hub 1101 and the pulley 1102.
The hub 1101 includes a boss portion 1101a on an inner periphery side, a rim portion 1101b on an outer periphery side, and a disk portion 1101c which connects the boss portion 1101a and the rim portion 1101b. The boss portion 1101a is fitted on one end of a crankshaft 1120 and is fixed with a bolt 1121.
The disk portion 1101c has a cylinder portion 1101d in a cylindrical shape which protrudes toward an outer side (a direction opposite to a direction toward a front cover 1122 of the engine) of the hub 1101 and is centered about an axis x, a hub-side projecting portion 1101p in an annular shape which protrudes toward the front cover 1122 and is centered about the axis x, and a recessed portion 1101e in a generally U-shape in cross-section which is formed to face the front cover 1122.
The boss portion 1101a of the hub 1101 attached to the crankshaft 1120 is in a state of being inserted through a through hole 1123 in the front cover 1122 from outside the engine.
The oil seal 1110 is press fitted in the through hole 1123 between the boss portion 1101a and the front cover 1122. A seal lip 1111 of the oil seal 1110 abuts slidably and liquid-tightly on an outer peripheral surface of the boss portion 1101a and hermetically seals a void between the damper pulley 1100 and the front cover 1122.
The front cover 1122 is arranged at a position spaced apart by a predetermined distance from the damper pulley 1100. A cover-side projecting portion 1122p in an annular shape which protrudes toward the hub 1101 and is centered about the axis x is formed at a portion of the front cover 1122 which faces the recessed portion 1101e of the hub 1101.
That is, the cover-side projecting portion 1122p is in a state of being arranged on the inner periphery side closer to the axis x than the hub-side projecting portion 1101p of the hub 1101, and the cover-side projecting portion 1122p is in a state of being inside the recessed portion 1101e of the hub 1101.
In this case, the hub-side projecting portion 1101p of the hub 1101 and the cover-side projecting portion 1122p of the front cover 1122 overlap spatially in a radial direction to form a labyrinth seal. By means of the labyrinth seal structure, the sealing structure with the damper pulley 1100 and the oil seal 1110 complicates a route of entry of dust from the outside as a measure to inhibit entry of such dust (see, for example, Japanese Patent Application Publication No. 2011-241891).